Copolymers comprising ethylene, vinyl esters and esters of (meth)acrylic acid, their formulations and use as pour point depressant, wax inhibitor and flow enhancer for crude oils

ABSTRACT

Copolymers comprising ethylene, vinyl esters, in particular vinyl acetate and esters of (meth)acrylic acid, selected from esters comprising branched alkyl, cyclic alkyl or optionally alkyl substituted aryl moieties and having a weight average molecular weight of 35,000 g/mol to 150,000 g/mol, formulations of such copolymers in organic solvents and their use as pour point depressant, wax inhibitor and flow enhancer for crude oils.

The present invention relates to copolymers comprising ethylene, vinylesters, in particular vinyl acetate and esters of (meth)acrylic acid,selected from esters comprising branched alkyl, cyclic alkyl oroptionally alkyl substituted aryl moieties and having a weight averagemolecular weight of 35,000 g/mol to 150,000 g/mol, formulations of suchcopolymers in organic solvents and their use as pour point depressant,wax inhibitor and flow enhancer for crude oils.

Underground mineral oil formations typically have relatively hightemperatures. After the production of the crude oil to the surface, thecrude oil produced therefore cools down to a greater or lesser degreeaccording to the production temperature and the storage or transportconditions.

According to their origin, crude oils have different proportions ofwaxes, which consist essentially of long-chain n-paraffins. According tothe type of crude oil, the proportion of such paraffins may typically be1 to 30% by weight of the crude oil. When the temperature goes below aparticular level in the course of cooling, the paraffins cancrystallize, typically in the form of platelets. The precipitatedparaffins considerably impair the flowability of the oil. Theplatelet-shaped n-paraffin crystals can form a kind of house-of-cardsstructure which encloses the crude oil, such that the crude oil ceasesto flow, even though the predominant portion is still liquid. The lowesttemperature at which a sample of an oil still just flows in the courseof cooling is referred to as the “pour point”. For the measurement ofthe pour point, standardized test methods are used. Precipitatedparaffins can block filters, pumps, pipelines and other installations orbe deposited in tanks, thus entailing a high level of cleaning.

The deposit temperature of oil deposits is generally above roomtemperature, for example 40° C. to 100° C. Crude oil is produced fromsuch deposits while still warm, and it naturally cools more or lessquickly to room temperature in the course of or after production, orelse to lower temperatures under corresponding climatic conditions.Crude oils may have pour points above room temperature, so such thatcrude oils of this kind may solidify in the course of or afterproduction.

It is known that the pour point of crude oils can be lowered by suitableadditives. This can prevent paraffins from precipitating in the courseof cooling of produced crude oil. Suitable additives firstly prevent theformation of said house-of-cards-like structures and thus lower thetemperature at which the crude oil solidifies. In addition, additivescan promote the formation of fine, well-crystallized, non-agglomeratingparaffin crystals, such that undisrupted oil transport is ensured. Suchadditives are referred to as pour point depressants or flow improvers.

It is known in the art to use copolymers of ethylene and vinyl acetateas pour point depressant for improving cold flow properties of crude oiland mineral oil products such as disclosed for instance in GB 900,202 A,GB 1,147,904 A, GB 1,403,782 A and EP 003 489 A1.

However, the performance of ethylene-vinyl acetate copolymers aloneoften is not sufficient and the solubility of such polymers inhydrocarbons often is not sufficient. Therefore, a lot of attempts havebeen made in order to improve the performance of such ethylene-vinylacetate copolymers,

DE 20 47 448 A discloses additives for lowering viscosity inparaffin-based crude oils. The additives are mixtures of polyvinylethers and ethylene-vinyl acetate copolymers.

It is furthermore known to modify ethylene-vinyl acetate copolymers bycopolymerizing by acrylates, in particular long-chain acrylates in thepresence of ethylene-vinyl acetate copolymers thereby yielding graftpolymers in which at least a part of the poly acrylate has been graftedonto the ethylene-vinyl acetate copolymer. Examples of that techniqueare disclosed in EP 486 836 A1 and U.S. Pat. No. 4,608,411.

However, the production of graft polymers needs an additionalmanufacturing step. It is desirable to avoid such an additional step.

It is furthermore known to use additional comonomers besides ethyleneand vinyl acetate, in particular (meth)acrylates and vinyl estersdifferent from vinyl acetate.

DE 19 02 925 A discloses copolymers of 40 % to 89 % by wt. of ethylene,10 % to 40 % by wt. of vinyl esters of monocarboxylic acids having 2 to4 carbon atoms, and 1 to 30% by wt. of C₁₀ to C₂₂ alkyl esters of(meth)acrylic acid or vinyl esters of monocarboxylic acids having 10 to22 carbon atoms having a number average molecular weight of 1,000 to50,000, preferably 1,500 to 5,000. DE 190 29 25 A furthermore disclosesthe use of such copolymers as pour point depressants for crude oildistillates.

U.S. Pat. No. 4,156,434 discloses a terpolymer of 60% to 89% by wt.ethylene, 8% to 25% by wt. vinyl acetate, and 3% to 15% by wt. of alinear or branched C₁₂ to C₂₂ alkyl ester of (meth)acrylic acid having anumber average molecular weight of 12,000 to 37,000. The publicationdoes not disclose any specific C₁₂ to C₂₂ alkyl esters used. U.S. Pat.No. 4,156,434 furthermore discloses the use of such terpolymers as pourpoint depressant for gas oils.

EP 493 769 A1 discloses terpolymers of 40% to 94% by wt. of ethylene, 5to 35% of vinyl acetate and 1% to 25% of neononane carboxylic acid vinylesters or neodecane carboxylic acid vinyl esters (i.e. branched C₉ orC₁₀ carboxylic acid vinyl esters) having a number average molecularweight of 500 to 5,000 g/mol and their use as additives for mineral oildistillates.

WO 96/07718 A1 discloses an oil composition comprising a terpolymer ofethylene and two different carboxylic acid vinyl esters, one of thembeing the vinyl ester of a C₁ to C₅ carboxylic acid and the other onebeing a branched C₉ to C₁₅ carboxylic acid.

WO 96/17905 A1 discloses an oil-soluble additive comprising a terpolymerof ethylene and vinyl esters H₂C═CHOOR or acrylates H₂C═CH—COOR, whereinR is a C₁ to C₄ alkyl group and vinyl esters H₂C═CHOOR′ or acrylatesH₂C═CH—COOR′ wherein R′ is a tertiary alkyl group having 8 or morecarbon atoms.

WO 2005/054314 A2 discloses the use of polymers comprising 60 to 98 mol% α-olefines, preferably ethylene, 1 to 20 mol % vinyl esters,preferably vinyl acetate and 1 to 20 mol % esters of α,β-unsaturatedcarboxylic acids, preferably C₁ to C₂₀ esters as additives for fuel oilsand lubricants. The number average molecular weight is 1,000 to 20,000,preferably 1,500 to 5,000. The weight average molecular weight may be1,000 to 30,000 and M_(w)/M_(n) may be from 1,5 to 5. A copolymer ofethylene, vinyl acetate and 2-ethylhexyl acrylate is most preferred.

WO 2009/106744 A2 discloses the use of a terpolymer comprising 78% to87% by mol ethylene, 12% to 18% by mol vinyl acetate and 1% to 4% by molacrylates, preferably 2-ethylhexyl acrylate as additive for fuel oils.Preferably, the weight average molecular mass is 3,000 to 30,000.

The cited documents focus on the use of terpolymers of ethylene, vinylacetate and further comonorners as additives for fuel oils, mineral oilsand/or destillates of crude oil. It were desirable to use such class ofpolymers also as additives for crude oil, in particular as pour pointdepressant for crude oil, wax inhibitors for crude oil or rheologymodifiers for crude oil.

However, there are different requirements to such additives for crudeoil compared to additives fuel oils, mineral oils and/or destillates ofcrude oil which makes it difficult to use such known additives withoutmodifications for crude oil.

Additives for crude oil are necessarily used at the production sites ofcrude oil. Such production sites also may be offshore platforms whichfurthermore may be located in cold regions, e.g. arctic regions. Pourpoint depressants are generally supplied as concentrated solutions andcan be formulated for use in the desired manner by the users on site.The products supplied should be liquid in order to avoid melting onsite, and the solutions should also remain stable over a long period andnot have a tendency to phase separation, such that they can be storedwith great simplicity.

It was therefore an object of the present invention to provide acopolymer comprising ethylene, a vinyl ester, and a (meth)acrylate whichcan be easily provided as formulations in non-polar solvents having asufficient stability during transport, storage and use even in coldenvironments and which have a good performance as pour point depressant,wax inhibitors and rheology modifiers for crude oil.

Accordingly, copolymer (A) at least comprising ethylene, a vinyl ester,and a (meth)acrylate have been found wherein the copolymer (A) at leastcomprises

-   -   (M1) 83.5 mol % to 96.5 mol % of ethylene,    -   (M2) 3 mol % to 11.5 mol % of at least one vinyl ester of the        general formula H₂C═CH—O—(O)C—R¹ (I) where R¹ is H or a C₁- to        C₄ alkyl moiety, and    -   (M3) 0.5 mol % to 5 mol % of a (meth)acrylate of the general        formula H₂C═C(R²)—COOR³ wherein R² is H or methyl, and R³ is        selected from the group of        -   R^(3a): branched alkyl moieties having 4 to 18 carbon atoms,        -   R^(3b): cyclic alkyl moieties having 5 to 12 carbon atoms,            and        -   R^(3c): optionally alkyl substituted aryl moieties having 6            to 12 carbon atoms,            and wherein the weight average molecular weight M, of the            copolymer (A) is 35,000 g/mol to 150,000 g/mol.

In a second aspect of the invention, a polymer composition (X) has beenfound at least comprising

-   -   at least one copolymer (A) as defined above, and    -   at least one organic solvent (B),        wherein the concentration of the copolymer (A) is 5 to 25% by        weight with respect to the sum of all components of the polymer        composition (X).

In a third aspect of the invention it has been found to use thecopolymers (A) as defined above as pour point depressants, waxinhibitors and rheology modifiers for crude oil.

Specific details of the invention are as follows:

Copolymer (A)

Copolymer (A) according to the invention comprises as monomers at leastethylene (monomer M1), a vinyl ester (monomer M2), and a (meth)acrylate(monomer M3).

Copolymer (A) comprises 83.5 mol % to 96.5 mol % of ethylene (monomerM1), preferably 85 mol % to 95 mol %, more preferably 86 mol % to 93 mol%, and most preferably 88 mol % to 92 mol %.

Copolymer (A) furthermore comprises 3 mol % to 11.5 mol % of at leastone vinyl ester (monomer M2) of the general formula H₂C═CH—O—(O)C—R¹ (I)where R¹ is H or a C₁- to C₄ alkyl moiety. Preferably R¹ is methyland/or ethyl and more preferably R¹ is methyl. Preferably, the amount ofthe vinyl ester(s) is 4 mol % to 10.5 mol %.

Copolymer (A) furthermore comprises 0.5 mol % to 5 mol % of at least one(meth)acrylate (monomer M3) of the general formula H₂C═C(R²)—COORSwherein R² is H or methyl, and R³ is at least one group selected fromthe group of R^(3a), R^(3b), and R^(3c). Preferably, the amount of(meth)acrylates is 0.5 mol % to 4 mol %.

The moieties R^(3a) are branched alkyl moieties having 4 to 18 carbonatoms, preferably 5 to 11 carbon atoms and more preferably 8 to 10carbon atoms. Examples of branched alkyl moieties R^(3a) comprise2-methylpropyl-, t-butyl-, 3-methylbutyl-, 2,2′-dimethylpropyl-,2-ethylhexyl-, 2-propylheptyl-, i-nonyl-, i-decyl-, i-undecyl-,i-dodecyl-, and i-heptadecyl-moieties, preference being given to2-ethylhexyl and 2-propylheptyl moieties. Most preferably, R^(3a) is a2-propylheptyl moiety.

The moieties R^(3b) are cyclic alkyl moieties having 5 to 12 carbonatoms, preferably 6 to 10 carbon atoms. Cyclic alkyl moieties may bemonocyclic or polycyclic, for example bicyclic. They may be furthermoresubstituted with linear and/or branched alkyl moieties. Examples ofcyclic alkyl moieties R³b comprise cyclopentyl-, cyclohexyl-,4-methylcyclohexyl-, cycloheptyl-, bicyclo[2.2.1]heptyl-,bicyclo[2.2,2]octyl- or 2-(1,7,7-trimethyl)bicycle[2.2.1]heptyl-moieties. Preferably, R^(3b) is a cyclohexyl moiety.

The moieties R^(3c) are optionally alkyl substituted aryl moietieshaving 6 to 12 carbon atoms. Examples comprise phenyl-, benzyl- or2-phenyl ethyl- moieties.

Preferably, R³ is selected from R^(3a) and R^(3b), more preferably, R³is R^(3a).

Besides the monomers M1, M2, and M3 copolymer (A) may comprise furthermonomers M4. Suitable monomers M4 are ethylenically unsaturated monomerswhich are copolymerizable with the monomers M1; M2, and M3, Such furthermonomers M4 may be used to fine tune the properties of the polymer.

Examples of monomers M4 comprise olefins, in particular α-olefines otherthan ethylene, for example propene, 1-butene or isobutene, vinyl estersH₂C═CH—O—(O)C—R⁴ (IV), wherein R⁴ is a hydrocarbon moiety having morethan 4 carbon atoms, in particular 5 to 20 carbon atoms, and(meth)acrylates H₂C═C(R²)—COOR⁵(V), wherein R² has the meaning asdefined above and R⁵ is a moiety other than R³, for example linear alkylmoieties having 1 to 22 carbon atoms, branched alkyl moieties havingmore than 12 carbon atoms, in particular 12 to 22 carbon atoms, and/oroptionally alkyl substituted aryl moieties having more than 12 carbonatoms, in particular 12 to 22 carbon atoms.

The amount of such additional monomers M4 is from 0% to 12,5 mol %,preferably from 0 to 10 mol %, more preferably 0 to 5 mol %, and in themost preferred embodiment no additional monomers M4 are present.

The copolymers (A) according to the invention have a weight averagemolecular weight NA, of 35,000 g/mol to 150,000 g/mol, preferably 50,000g/mol to 120,000 g/mol, and more preferably 60,000 g/mol to 110,000g/mol, and for example 70,000 g/mol to 100,000 g/mol.

The polydispersity M_(w)/M_(n) (M_(n): number average molecular weight)may be from 2 to 9, preferably from 3 to 7.

In one embodiment of the invention, copolymer (A) comprises 87 mol % to93 mol % ethylene, 4 mol % to 10 mol % of vinylacetate and 1 mol % to 4mol % of 2-propylheptyl(meth)acrylate, More preferably, copolymer (A)consists of such monomers. In a preferred embodiment such a polymer mayhave a weight average molecular weight of 60,000 g/mol to 150,000 g/mol,preferably 60,000 g/mol to 120,000 g/mol, more preferably from 65,000g/mol to 100,000 g/mol and for example from 70,000 g/mol to 90,000g/mol. The polydispersity M_(w)/M_(n) of such specific copolymers (A)may preferably be from 3 to 7.

In another embodiment of the invention, copolymer (A) comprises 87 mol %to 93 mol % ethylene, 4 mol % to 10 mol % of vinylacetate and 1 mol % to4 mol % of 2-ethylhexyl(meth)acrylate. More preferably, copolymer (A)consists of such monomers.

In another embodiment of the invention, copolymer (A) comprises 87 mol %to 93 mol % ethylene, 4 mol % to 10 mol % of vinylacetate and 0.5 mol %to 4 mol % of cyclohexyl(meth)acrylate. More preferably, copolymer (A)consists of such monomers.

Manufacture of Copolymers (A)

The copolymers (A) according to the invention can be manufactured byradical polymerization under high-pressure conditions using suitableinitiators for radical polymerization for example in stirredhigh-pressure autoclaves or in high-pressure tube reactors such as themethods described in WO 2005/054314 A2. Preparation of the copolymer (A)in stirred high-pressure autoclaves is preferred. Stirred high-pressureautoclaves are known per se and a description may be found in Ullmann'sEncyclopedia of Industrial Chemistry 5^(th) edition, keywords: waxes,Vol. A 28, p. 146 ff., Verlag Chemie Weinheirn, Basel, Cambridge, NewYork, Tokyo, 1996. They usually have a length/diameter ratio in therange from 5:1 to 30:1, preferably from 10:1 to 20:1. The high-pressuretube reactors which can also be employed are likewise described in saidcitation.

Suitable pressure conditions for the polymerization are from 1000 to3000 bar, preferably from 1500 to 2500 bar. The reaction temperaturesare, for example, in the range from 160° C. to 320° C., preferably inthe range from 180 to 260′C.

Useful initiators for free-radical polymerization are customaryfree-radical initiators such as organic peroxides, oxygen or azocompounds. Also suitable are mixtures of a plurality of free-radicalinitiators are also useful. Suitable peroxides are disclosed in U.S.2007/0094920 A1, paragraphs [0068], [0069], and [0070]. Particularlyuseful peroxides are di-tert-butyl peroxide, tert-butyl peroxypivalate,tert-butyl peroxyisononanoate, tert-amylperoxipivalate and dibenzoylperoxide and mixtures thereof. An azo compound which may be mentioned byway of example is azobisisobutyronitrile (“AIBN”). Free-radicalinitiators are introduced in amounts customary for polymerizations.

Optionally, the polymerization can be carried out in the presence of oneor more regulators (chain transfer agents) for controlling the molecularweight of the copolymers (A). Suitable regulators are disclosed in U.S.2007/0094920 A1, paragraphs [0056] to [0065]. Particularly usefulregulators are H₂, propene, butene, propion aldehyde, ormethylethylketone.

The amount of the regulator used can be chosen by the skilled artisanaccording to his/her needs. In order to achieve the desired weightaverage molecular weight M_(w) 30,000 g/mol to 150,000 g/mol it isfrequently advisable to limit the amount of regulator to an amount ofnot more than 0.6% by wt. relating to the total amount of all comonomersused.

In one embodiment of the invention, the amount of regulator is 0 to 0.2%by wt. relating to the total amount of all comonomers used. In anotherembodiment of the invention no regulator is used.

In a preferred method, the inventive copolymers (A) are prepared in sucha manner that ethylene is compressed by a gas compressor toapproximately 250 bar and in parallel a mixture of the comonomers M2,M3, and optionally M4 and optionally at least one regulator are alsocompressed separately by a pump to approximately 250 bar.

Both, ethylene and the comonomer mixture are mixed at a pressure ofapproximately 250 bar and thereafter the mixture is compressed by ahypercompressor to a pressure of about 1,700 to 2,200 bar. The monomersand the regulator are now dissolved in supercritical ethylene, Themixture having a temperature from 20° C. to 50° C., preferably 25° C. to35° C. is passed, preferably continuously, through a stirred autoclavewhich is maintained at a pressure of 1,500 to 2,500 bar, for example1,600 to 2,200 bar. The initiator which generally is dissolved in asuitable solvent, for example isododecane or methylethylketone is alsofed—preferably continuously—into the stirred autoclave, which thecomonomers are passing through thus maintaining the temperature in thisstirred autoclave chosen by the skilled artisan, for example at 180° C.to 260° C. as indicated above.

The polymer obtained after decompression of the reactor may be isolatedin a customary manner, Examples of isolation techniques includeunder-water pelletizing of the melt or the melt may be dissolveddirectly in a suitable solvent.

Modifications to this method are of course possible and can beundertaken by those skilled in the art without unreasonable effort, Forexample, the comonomers and the regulator can be separately metered intothe reactor or the reaction temperature may be varied during theprocess. For instance, also a tubular reactor may be used instead of astirred autoclave in the process described above,

Polymer Composition (X)

The polymer composition (X) according to the invention comprises atleast one copolymer (A) as described above and at least one organicsolvent (B). The copolymers (A) should be homogeneously dispersed,preferably dissolved in the organic solvent (B). It is of course alsopossible to use mixtures of different organic solvents (B).

The organic solvents (B) may, for example, be nonpolar solventscomprising saturated aliphatic hydrocarbyl groups, preferably thosehaving a flashpoint ≥60° C. Examples of such solvents comprise saturatedaliphatic hydrocarbons, saturated aliphatic alcohols or esters ofsaturated aliphatic carboxylic acids and saturated aliphatic alcohols,preferably each having a flashpoint ≥60° C. Examples of alcoholscomprise aliphatic alcohols having at least 8 carbon atoms, such as1-octanol, 1-decanol or 1-dodecanol. Examples of esters comprise estersof saturated fatty acids having at least 8 carbon atoms with saturatedaliphatic alcohols, for example methyl laurate or methyl stearate.Technical mixtures of various aliphatic esters are commerciallyavailable. In a further embodiment of the invention, it is possible touse esters of aliphatic or cycloaliphatic dicarboxylic acids, forexample dialkyl esters of cyclohexane-1,2-dicarboxylic acid, such asdiisononyl cyclohexane-1,2-dicarboxylate.

In a preferred embodiment of the invention, organic solvents (B)comprise hydrocarbons or a hydrocarbon mixture. These may be aliphatic,cycloaliphatic and/or aromatic hydrocarbons.

Preference is given to hydrocarbons or hydrocarbon mixtures having aflashpoint ≥60° C. The hydrocarbons may be used as a mixture ofhydrocarbons with other organic solvents as outlined above. Suchmixtures preferably comprise at least 50% by weight of hydrocarbons.Most preferably, only hydrocarbons or a hydrocarbon mixture are used asorganic solvent (B).

The hydrocarbons may, for example, be saturated aliphatic solvents orsolvent mixtures. These may be either paraffinic or naphthenic, i.e.saturated cyclic, hydrocarbons. Preference is given to high-boilingaliphatic hydrocarbons having a boiling point of at least 175° C. andpreferably a flashpoint ≥60° C. Suitable hydrocarbons having aflashpoint ≥60° C. comprise, for example, n-undecane (flashpoint 60° C.,boiling point 196° C.) or n-dodecane (flashpoint 71° C., boiling point216° C.). It is possible with preference to use technical mixtures ofhydrocarbons, for example mixtures of paraffinic hydrocarbons, mixturesof paraffinic and naphthenic hydrocarbons or mixtures of isoparaffins.It will be apparent to those skilled in the art that technical mixturesmay still comprise small residues of aromatic or unsaturatedhydrocarbons.

The hydrocarbons may also be aromatic solvents or solvent mixtures. Inone embodiment of the invention, the hydrocarbons are toluene or asolvent mixture comprising toluene. In a further embodiment, thehydrocarbons are high-boiling aromatic hydrocarbons having a boilingpoint of at least 175° C. and preferably a flashpoint ≥60° C. It ispossible with preference to use technical mixtures of aromatichydrocarbons. Technical mixtures of aromatic solvents are commerciallyavailable, for example technical mixtures of the Shellsol® A series orthe Solvesso® series.

The polymer composition (X) is prepared in the usual manner bydispersing or dissolving at least one copolymer (A) in at least oneorganic solvent (B). This may be done by dissolving solid copolymer (A),for instance granules of copolymer (A) in at least one organic solvent(B). In one embodiment the polymer melt obtained from polymerization maybe directly dissolved in at least one organic solvent (B).

Besides the copolymer(s) (A) and the organic solvent(s) (B) the polymercomposition (X) may of course comprise further components.

Examples of such further components include additives which may be usedin the ready-for-use formulation such as the wax inhibitors as describedbelow.

Specific examples of further components include poly(meth)acrylates,polymers comprising isobutene, α-olefines, for example copolymers ofmaleic acid anhydride and styrene, copolyrners of maleic acid anhydrideand vinylacetate, which may optionally be further reacted alcohols andamines, copolymers of maleic acid anhydride and (meth)acrylatescopolymers, Copolymers of fumaric acid esters and vinyl acetate,styrene-butadiene based copolymers, or alkylphenolformaldehyde resins.

The concentration of the copolymer (A) may be 5 to 35% by weight,preferably 10 to 30% by weight with respect to the sum of all componentsof the polymer composition (X).

Use of the Copolymers (A)

The copolymers (A) and/or the polymer compositions (X) may be used invarious oilfield applications by adding them and/or suitableformulations thereof to crude oil.

Use as Pour Point Depressants

In one embodiment of the invention the copolymers (A) can be used aspour point depressants for crude oil by adding at least a copolymer (A)to the crude oil.

Pour point depressants reduce the pour point of crude oils. The pourpoint refers to the lowest temperature at which a sample of an oil, inthe course of cooling, still just flows. For the measurement of the pourpoint, standardized test methods are used.

Preferably, a suitable formulation comprising at least a copolymer (A)and at least one solvent is added to the crude oil. Suitable solventsmay be selected from water, polar or nonpolar organic solvents. Thecopolymer(s) (A) may be dissolved or dispersed in the solvent. Theformulations may of course comprise further components such as forinstance surfactants.

In one embodiment, the copolymers (A) can be used as pour pointdepressants for crude oil by adding a suitable formulation comprising atleast a copolymer (A) and an organic solvent capable of dissolving thecopolymer(s) (A) to the crude oil.

The skilled artisan may select suitable organic solvents according tohis/her needs. Preferably, non-polar organic solvents, in particularorganic solvents (B) as defined above may be used. The concentration ofthe copolymers (A) may also be selected by the skilled artisan an may befrom 0,1 % by weight to 35% by weight of copolymers (A) in theready-for-use formulation.

The formulation to be used may additionally comprise further components.For example, additional wax dispersants can be added to the formulation.Wax dispersants stabilize paraffin crystals which have formed andprevent them from sedimenting. The wax dispersants used may, forexample, be alkylphenols, alkylphenol-formaldehyde resins ordodecylbenzenesulfonic acid.

In one preferred embodiment, the formulation comprising organic solventscomprises a composition (X). The polymer composition (X) may be used assuch or further components as outlined above and/or further organicsolvents, in particular further organic solvents (B) may be added beforeuse.

The formulation to be used may be formulated at or close to the site ofuse, i.e. at or close to the oilfield or it may be formulated in achemical plant distant from the site of use and then provided to thesite of use. In one embodiment the site of use is an offshore platform.

In one preferred embodiment of the invention a polymer composition (X)is provided to the site of use, optionally further formulated and thenused. It is the advantage of the polymer composition (X) that it is aconcentrate thus minimizing transport costs but remains neverthelessliquid even at low temperatures so that it can be used without the needto melt it before use.

The inventive use is effected by adding the formulations comprisingcopolymer (A) and optionally comprising further components to the crudeoil. The formulation should be added as long as the crude oil has atemperature greater or equal to its pour point.

The formulations are typically used in such an amount that the amount ofall copolymers (A) together added is 50 to 3000 ppm based on the oil.The amount is preferably 100 to 1500 ppm, more preferably 250 to 600 ppmand, for example, 300 to 600 ppm.

In a preferred embodiment of the invention the formulation is injectedinto a crude oil pipeline.

The injection can preferably be effected at the oilfield, i.e. at thestart of the crude oil pipeline, but the injection can of course also beeffected at another site. More particularly, the pipeline may be oneleading onshore from an offshore platform. Explosion protection isparticularly important on offshore platforms, therefore formulationsbased on organic solvents having a flashpoint ≥60° C. accordinglysimplify working quite considerably. Moreover, the cooling of crude oilin underwater pipelines leading onshore from an offshore platform isnaturally particularly rapid, especially when the pipelines are in coldwater, for example having a water temperature of less than 10° C.

In a further preferred embodiment of the invention the formulation isinjected into a production well. Here too, the production well mayespecially be a production well leading to an offshore platform. Theinjection is preferably effected approximately at the site where oilfrom the formation flows into the production well. In this way, thesolidification of the crude oil in the production well or an excessiveincrease in its viscosity can be prevented.

In another embodiment of the invention the copolymers (A) are used aspour point depressant and/or paraffin inhibitor for crude oil by addingemulsions and/or dispersions of at least one copolymer (A) in a suitablesolvent or solvent mixture to the crude oil.

Examples of suitable solvents for such emulsions or dispersions includewater, polar organic solvents miscible with water, including but notlimited to alcohols such as methanol, ethanol, propanol, ethyleneglycol, propylene glycol. Of course mixtures of two or more or moresolvents may be used, for instance a mixture comprising water and anorganic solvent miscible with water.

In a dispersion, the copolymer (A) is dispersed in a suitable solvent orsolvent mixture. In an emulsion, a mixture, preferably a solution of thecopolymer(s) (A) in a suitable solvent is emulsified in another solventwhich is not miscible with the first solvent. As an example, thecopolymer(s) (A) may be dissolved in a non-polar organic solvent and thesolution is emulsified in water and/or a polar organic solvent. In oneembodiment, a polymer composition (X) as described above may beemulsified in water and/or a polar organic solvent.

In addition, said emulsions and/or dispersions of at least one copolymer(A) comprise at least one emulsifier or a mixture of emulsifiers.Preferably, the amount of emulsifiers in a ready to use formulation isat least at least 10% by wt. with respect to the total of allcomponents, for example 10-20% by weight. Examples of suitableemulsifiers comprise anionic or non-ionic surfactants including but notlimited to ethoxylated fatty alcohols such as C_(16/18)-(EO)_(x)H with xfrom 5 to 50 or synthetic ethoxylated alcohols such as C₁₃-(EO)_(y)Hwith y from 5 to 50.

The concentration of the copolymers (A) in the emulsions or dispersionsmay be from 5 to 40% by wt. in a ready to use formulation.

Such emulsions and/or dispersions of at least one copolymer (A) in asuitable solvent or solvent mixture may be made by melting at least thecopolymer(s) (A), the emulsifier(s) and—if present—an organic solvent ina vessel until all ingredients form a homogeneous clear melt. Understirring, water and/or a polar organic solvent is added at 90° C. andstirring is continued until the formulation has been cooled down to roomtemperature.

In another embodiment such aqueous formulations may be made is bymelting at least the copolymer(s) (A), at least one emulsifier and —ifpresent —an organic solvent in a vessel until all ingredients form ahomogeneous clear melt. While stirring slowly with a low shear rate,water or a polar organic solvent is added at 90° C. and stirring iscontinued. During the cooling process, at least one further emulsifieris added to the formulation, then it is cooled down to room temperature.

Use as Wax Inhibitors

In a further embodiment of the invention, the copolymers (A), inparticular the above-detailed formulations, especially the formulationscomprising polymer compositions (X) are used to prevent wax deposits onsurfaces in contact with crude oil. The use is effected by adding atleast one of the formulations detailed above to the crude oil. Preferredformulations have already been mentioned, and the manner of use is alsoanalogous to the use as a pour point depressant. In addition, it is ofcourse also possible to use further formulations which act as waxinhibitors.

It is an advantage of the copolymers (A) according to the presentinvention that they are suitable for use as pour point depressants andalso for use as wax inhibitors. Therefore it is not necessary to mixpour point depressants and wax inhibitors if both effects are desired bythe skilled artisan but using one component is sufficient.

Use as Rheology Modifiers

In a further embodiment of the invention, the copolymers (A), inparticular the above-detailed formulations, especially the formulationscomprising polymer compositions (X) are used as rheology modifiers inorder to improve the flowing properties of crude oil, e.g. of oilflowing through pipelines to lower its viscosity thereby facilitatingits transport. For this purpose the copolymers, preferably a formulationof the copolymers as detailed above may be added to the crude oil.

The following examples are intended to illustrate the invention indetail:

Part A: Manufacture of the Copolymers (A) and Comparative Copolymers

The copolymers (A) and comparative copolymers were manufactured byradical polymerization of ethylene, vinyl acetate and the respective(meth)acrylates under high pressure in a stirred high-pressure autoclavein a continuous process. Ethylene (12,0 kg/h) was pressurized to 250 barby a pre-compressor. Vinyl acetate, the respective (meth)acrylate usedand propionaldehyde as regulator were pressurized by middle pressurepumps also until 260 bar. The amounts of the comonomers andpropionaldeyde are provided by table 1. The ethylene feed and thecomonomer mixture were compressed together with a hypercompressor toabout 1,700 bar and the mixture was fed in the autoclave. Separately,tert-amylperoxypivalate dissolved in isododecane was also pressurizedwith another high pressure pump to 1,700 bar and also fed into theautoclave. The temperature in autoclave was kept constantly at around220° C. After the polymerization, the polymer is separated from the freemonomers by reducing the pressure very rapidly to 1 to 20 bar. Theresulting copolymer is collected as a melt in a heated product tank(200° C.), For use it may be removed and solidified.

The properties of the collected copolymers are summarized in Table 2.

TABLE 1 Feed of monomers and regulators into reactor polymerization,i-pentyl-, i-nonyl-, i-tridecyl-, and i-heptadecyl moieties are branchedalkyl groups. vinyl propion- acetate (meth)acrylate aldehyde Yield No.[l/h] type [l/h] [ml/h] % C1 6.5 — — — 20 C2 7.2 — — — 20 C3 6.33 — —102 21 C4 5.4 2-propylheptyl acrylate 0.9 910 21 C5 7.5 2-propylheptylacrylate 1.5 0 20 C6 2.57 methyl acrylate 0.42 27 20 C7 5.13 n-octylacrylate 0.27 50 20 C8 4.67 n-dodecyl acrylate 1.3 67 25 C9 5.21n-dodecyl acrylate 0.125 0 19 C10 5.2 n-dodecyl methacrylate 0.135 0 18C11 4.12 n-dodecyl methacrylate 0.46 74 25 C12 3.1 n-octadecyl acrylate0.2 0 20 C13 3.2 n-docosyl acrylate 0.2 0 21  1 5.1 2-propylheptylacrylate 0.34 0 21  2 4.9 2-propylheptyl acrylate 0.30 0 24  3 4.452-propylheptyl acrylate 1.15 82 21  4 4.54 cyclohexyl methacrylate 0.2639 20  5 5.52 cyclohexyl methacrylate 0.45 0 24  6 4.41 cyclohexylacrylate 0.72 98 21  7 5.13 2-ethylhexyl acrylate 0.27 43 22  8 3.382-ethylhexyl acrylate 0.91 105 21  9 5.1 i-pentyl acrylate 0.25 0 20 104.4 i-nonyl acrylate 1.2 0 21 11 4.6 i-tridecyl acrylate 1.3 0 21 12 3.2i-heptadecyl acrylate 0.2 0 23

TABLE 2 Composition of the copolymers synthesized, comparative examples2-propyl n-dodecyl vinyl heptyl methyl n-octyl n-dodecyl meth-n-octadecyl n-docosyl Mw M_(n) No. Ethylene acetate acrylate acrylateacrylate acrylate acrylate acrylate acrylate [g/mol] [g/mol] M_(w)/M_(n)C1 88.8 11.2 — — — — — — — 45700 8380 5.5 C2 86.2 13.8 — — — — — — —118000 20300 5.8 C3 89.4 10.4 — — — — — — — 35000 6500 5.4 C4 86.2 10.53.3 — — — — — — 7300 3000 2.4 C5 80 14 6 — — — — — — 41000 8200 5.0 C690.5 4.8 — 4.6 — — — — — 75000 9000 8.3 C7 91.4 7.4 — — 1 — — — — 450008500 5.3 C8 89.1 7.3 — — — 3.4 — — 49600 7710 6.4 C9 88.9 10.4 — — — 0.5— — — 81400 9780 8.3 C10 88.9 10.3 — — — — 0.5 — — 102400 17120 6.0 C1192.2 6.4 — — — — 1.3 — — 38000 5900 6.4 C12 90 9.4 — — — — — 0.3 — 760009030 8.4 C13 89.6 9.5 — — — — — — 0.6 75600 9040 8.4 Composition of thecopolymers synthesized, examples according to invention 2-propyl cyclocyclo 2-ethyl Vinyl heptyl hexyl hexyl hexyl i-pentyl i-nonyl i-tridecyli-heptadecyl Mw M_(n) No. Ethylene acetate acrylate methacrylateacrylate acrylate acrylate acrylate acrylate acrylate [g/mol] [g/mol]M_(w)/M_(n) 1 89.1 9.4 1.3 — — — — — — — 73000 10500 7.0 2 90 9 1 — — —— — — — 66700 21200 3.1 3 89.8 6.9 3.2 — — — — — — — 48600 7390 6.6 490.6 7.4 — 1.8 — — — — — — 34700 5880 5.9 5 88.1 8.7 — 2.9 — — — — — —66700 7860 8.5 6 90.2 7.4 — — 2.3 — — — — — 38800 6820 5.7 7 91.5 7.3 —— — 1 — — — 54900 7460 7.4 8 91.6 4.7 — — — 3.6 — — — — 39000 6660 5.9 991.5 7.2 — — — — 1.1 — — — 75000 9035 8.3 10  90.5 6.3 — — — — — 3.2 — —65000 10430 6.2 11  89.2 7.4 — — — — — — 3.3 — 50000 8200 6.1 12  90 9.4— — — — — — — 0.3 76900 9520 8.1Manufacture of Polymer Compositions (X)

100 kg of granulates of copolymer (A) No. 2 are dissolved in 900 kgSolvesso® 150 (a high-boiling aromatic hydrocarbon mixture fromExxonMobil Chemical Company, aromatics content >99% by vol., initialboiling point 184° C., flashpoint to ASTM D93 >61° C.) in a vessel (1,5m³). The mixture is heated at 80° C. and stirred with 60 rpm for 4hours.

After 4 hours the solution is completely homogenous dissolved. Polymercontent: 9.8% by wt.

Viscosity of the solution at 25° C.: 57 mPas (see table 3).

Solutions of the other copolymers (A) and solutions of comparativecopolymers were obtained in similar manner.

Part B: Test of the Properties of the Polymers Obtained

Molecular Weight Determination

The number-average molecular weight M and the weight-average molecularweight M_(w) of each of the copolymers obtained were determined by meansof gel permeation chromatography in tetrahydrofuran as the solvent usingpolystyrene standards. The values are compiled in table 2 and 3.

Determination of Viscosity in Aromatic Solvent

The viscosity of solutions of 10% by wt. of the copolymers (A) andcomparative polymers in Solvesso® 150 were measured at 25° C. using aBrookfield DV 111+ Rheometer using a constant shear rate and spindle#21. The results are summarized in table 3.

Determination of the Pour Point

The determination of the pour point was conducted to ASTM D97 “StandardTest Method for Pour Point of Petroleum Products. The pour point is theminimum temperature at which a sample of the oil used for the tests isstill just free-flowing. According ASTM D97, for this purpose, a sampleof the oil is cooled in steps of 3° C. each and the flowability istested after each step. For the tests, a crude oil from the “Landau”oilfield in south-west Germany (Wintershall Holding GmbH) having an APIgravity of 37 and a pour point of 27° C. was used. To determine thelowering of the pour point, the graft copolymers to be tested were usedto the oil in a concentration of 100 ppm, 300 ppm or 1500 ppm, in eachcase of polymer based on the crude oil. The values are compiled intable 1. Double or triple determinations were conducted on some samples.In these cases, all measurements are reported in the table. The resultsare summarized in table 3.

Determination of Viscosity of Crude Oil

For the tests, a crude oil from the “Landau” oilfield in south-westGermany (Wintershall Holding GmbH) having an API gravity of 37 and apour point of 27° C. was used. The viscosity in crude oil was measuredby a HAAKE RheoStress 6000 rheometer for each sample using a sampleadapter of cone and plate. The shear rate is constant.

The viscosity of the crude oil at 9° C. is 2500 mPas. Furthermore, theviscosity of crude oil comprising 100 ppm of the copolymers C1 to C13and 1 to 12 (added as 10% solution in xylene) and the viscosity of crudeoil comprising 300 ppm of copolymers C1 to C13 and 1 to 12 were measuredrespectively under the same conditions in order to study the influenceof the copolymers on the rheological properties of the oil. The resultsare summarized in table 3.

Wax Inhibition

The cold finger deposition test was utilized to determine the waxinhibition properties of the terpolymers. The wax inhibition wasdetermined by exposing the crude oil to a cold metal finger surface inthe presence and absence of the inhibitor. The amount and type of waxdeposited on the cold metal finger was used to determine waxingtendency.

For the tests, a crude oil from the “Landau” oilfield in south-westGermany (Wintershall Holding GmbH) having an API gravity of 37 and apour point of 27° C. was used. The test was started by conditioning theoil sample by heating to 80° C. and holding for 30 minutes to removethermal history. A water bath on the cold finger apparatus was adjustedso that the oil temperature is maintained at 35° C. The cold finger wasmaintained at 4° C. and the cold finger was inserted into oil sample.The test was run for 4 hours. The cold finger was removed the waxdeposit was removed with a paper towel. The wax deposit was weighed. Thewax test was repeated in the presence and absence of the copolymers C1to C13 and 1 to 12. The amount of copolymers used was 1000 ppm (added assolution of 10% copolymer in xylene) with respect to crude oil. Thepercent efficacy was calculated on the performance of paraffin inhibitoras compared to the baseline (i.e. the measurement without wax inhibitor

The results are summarized in table 3.

TABLE 3 Summary of results, *the viscosity of crude oil withoutadditives is 2500 mPas viscosity in Cold Vis- crude oil at finger Waxcosity Pour Point [° C.] 9° C.* [mPas] test wax in- Polymer composition[mol %] in amount of amount of depo- hibi- (meth)acrylaye solution M_(w)polymer [ppm] polymer [ppm] sition tion No. E Vac type amount [mPas][g/mol] 100 300 1500 100 300 [g] [%] C1 88.8 11.2 — — 79.5 45700 14 7.511 2000 1800 4.01 58 C2 86.2 13.8 — — 102 118000 12 9 9 2100 1500 3.8 60C3 89.4 10.4 — — 20 35000 18 18 12 2500 2334 3.5 58 C4 86.2 10.5 C10,branched 3.3 3 7300 27 26 19 2238 2679 7.9 18 C5 80 14 C10, branched 635 41000 25 24 23 2200 2100 3.5 58 C6 90.5 4.8 C1 4.6 45 75000 17 16 122233 1356 4.7 51 C7 91.4 7.4 C8, linear 1 50 45000 18 18 12 2450 1500 457 C8 89.1 7.3 C12, linear 3.4 20 49600 21 18 18 2499 1690 6 37 C9 88.910.4 C12, linear 0.5 50 81400 9 9 9 2139 1522 2.57 73 C10 88.9 10.3 C12,linear 0.5 130 102400 9 9 9 2400 1538 2.73 72 C11 92.2 6.4 C12, linear1.3 270 38000 15 13.5 13.5 2500 1010 3.8 60 C12 90 9.4 C18, linear 0.375 76000 12 9 9 2300 1300 3.5 62 C13 89.6 9.5 C22, linear 0.6 80 7560012 9 9 2350 1710 3.6 57 1 89.1 9.4 C10, branched 1.3 55 73000 9 9 6 17981346 1.88 80 2 90 9 C10, branched 1 57 66700 9 9 6 1500 1200 1.89 78 389.8 6.9 C10, branched 3.2 20 48600 18 12 12 1800 1805 1.87 80 4 90.67.4 C6, cyclic 1.8 40 34700 18 15 12 1992 1555 1.56 84 5 88.1 8.7 C6,cyclic 2.9 20 66700 17.5 12 9 1455 1448 1.23 87 6 90.2 7.4 C6, cyclic2.3 17 38800 19.5 16.5 15 1850 1259 1.36 86 7 91.5 7.3 C8, branched 1 5054900 16.5 15 13.5 1768  838 1.86 81 8 91.6 4.7 C8, branched 3.6 4539000 18 12 12 1582 1475 2.01 80 9 91.5 7.2 C5, branched 1.1 43 75000 1512 9 1553 1200 2.7 72 10 90.5 6.3 C9, branched 3.2 25 65000 16 12 9 14201150 2.5 73 11 89.2 7.4 C13, branched 3.3 30 50000 17 12 9 1512 1300 2.574 12 90 9.4 C17, branched 0.3 40 76900 12 12 9 1581 1567 2.3 77Comments on the Results Obtained:

The present application relates to copolymers comprising ethylene,vinylesters and and certain (meth)acrylic acid esters which arespecifically adapted for use in oilfield applications, in particular aspour point depressants, wax inhibitors, and rheology modifiers. Althoughsimilar (but not the same) copolymers are known for use in fuel oilapplications our examples demonstrate that certain conditions need to befulfilled in order to provide satisfying results in oilfieldapplications.

All copolymers (A) according to the invention show a wax inhibition ofmore than 70%, including examples 1 to 8 which show a wax inhibition ofat least 80%. Only two of the comparative examples have a wax inhibitionof 72%, resp. 73% while all the other comparative examples show a waxinhibition of not more than 62%, in the worst case only 18%.

In a similar manner, none of the comparative polymers added at aconcentration of 100 ppm to crude oil diminishes the viscosity of saidcrude oil at 9° C. (2500 mPas) to numbers of less than 2000 mPas whileall inventive copolymers yield less than 1850 mPas. The copolymercomprising 2-propylheptylacrylate (examples 1, 2, and 3) shows the bestperformance as pour point depressant.

A comparison of examples 1 and 2 with example 3 and with comparativeexample 4 shows the importance of a sufficient molecular weight.Comparative example 1 also comprises 2-propylheptylacrylate but has amolecular weight M_(w) of only 7,300 g/mol (which is well below thelower limit of 35,000 g/mol as required by our invention). Itsperformance as pour point depressant, wax inhibitor, and rheologymodifier is the worst of all examples but also comparative examples. Thebest examples 1 and 2 have a molecular weight M_(w) of 73,000 g/mol and66,700 g/mol respectively. Example 3 which also comprises2-propylheptylacrylate has a somewhat lower molecular weight of 48,600g/mol. While its performance as wax inhibitior and rheology modifierstill is very satisfying, its performance is no longer that good as thatof examples 1 and 2.

Comparative example 4 demonstrates the need of a sufficient amount ofethylene. The polymer comprises only 80 mol % ethylene (which is belowthe lower limit of 84 mol % ethylene required by our invention) and itsperformance as pour point depressant is as worse as that of comparativeexample 4.

Comparative example C7 shows that linear alkyl moieties are inferior ascompared to the branched of cyclic alkyl moieties of the presentinvention. The copolymer C7 comprises 1% of n-octyl acrylate while thecopolymer 7 comprises 1% of 2-ethylhexyl acrylate. While the performanceas pour point depressant is in about the same for both polymers, C7added at a concentration of 100 ppm does nearly not reduce the oilviscosity at all, while copolymer 7 already significantly reduces it.Also at a concentration of 300 ppm the performance of copolymer is farbetter than that of C7. Furthermore, copolymer C7 has not a goodperformance as wax inhibitor (57%), while polymer 7 has an excellentperformance (81%).

Similar observations may be made by comparing a linear C₁₂ acrylate(copolymer C8) with a branched C₁₃ acrylate (copolymer 11). Copolymer 11shows a better performance as pour point depressant but also as waxinhibitor and rheology modifier.

It is the advantage of the copolymers (A) according to the inventionthat they not only act as pour point depressants for crude oil butsimultaneously as wax inhibitors and rheology.

The invention claimed is:
 1. A method comprising adding a pour pointdepressant for crude oil comprising a copolymer (A) to the crude oil;wherein the copolymer (A) comprises (M1) 83.5 mol % to 96.5 mol % ofethylene, (M2) 3 mol % to 11.5 mol % of at least one vinyl ester of theformula H₂C═CH—O—(O)C—R¹ (I) where R¹ is H or a C₁- to C₄ alkyl moiety,and M3) 0.5 mol % to 5 mol % of a (meth)acrylate of the formulaH₂C═C(R²)—COOR³ wherein R² is H or methyl, and R³ is selected from thegroup consisting of R^(3a): branched alkyl moieties having 4 to 18carbon atoms, R^(3b): cyclic alkyl moieties having 5 to 12 carbon atoms,and R^(3c): aryl moieties having 6 to 12 carbon atoms which areoptionally alkyl substituted, and wherein the copolymer (A) has a weightaverage molecular weight M_(w) of 35,000 g/mol to 150,000 g/mol.
 2. Themethod according to claim 1, wherein R¹ is a methyl moiety.
 3. Themethod according to claim 1, wherein R^(3a) has 5 to 11 carbon atoms. 4.The method according to claim 1, wherein R^(3a) has 8 to 10 carbonatoms.
 5. The method according to claim 1, wherein R^(3b) has 6 to 10carbon atoms.
 6. The method according to claim 1, wherein R³ is selectedfrom the group consisting of R^(3a) and R^(3b).
 7. The method accordingto claim 1, wherein R³ is R^(3a).
 8. The method according to claim 1,wherein the weight average molecular weight M_(w) of the copolymer (A)is 50,000 g/mol to 120,000 g/mol.
 9. The method according to claim 1,wherein an emulsion or dispersion of at least one copolymer (A) in asolvent or solvent mixture to the crude oil.
 10. A method comprisingadding a formulation comprising at least one copolymer (A) and anorganic solvent to crude oil; wherein the copolymer (A) comprises (M1)83.5 mol % to 96.5 mol % of ethylene, (M2) 3 mol % to 11.5 mol % of atleast one vinyl ester of the formula H₂C═CH—O—(O)C—R¹ (I) where R¹ is Hor a C₁- to C₄ alkyl moiety, and (M3) 0.5 mol % to 5 mol % of a(meth)acrylate of the formula H₂C═C(R²)—COOR³ wherein R² is H or methyl,and R³ is selected from the group consisting of R^(3a): branched alkylmoieties having 4 to 18 carbon atoms, R^(3b): cyclic alkyl moietieshaving 5 to 12 carbon atoms, and R^(3c): aryl moieties having 6 to 12carbon atoms which are optionally alkyl substituted, and wherein thecopolymer (A) has a weight average molecular weight M_(w) of 35,000g/mol to 150,000 g/mol.
 11. The method according to claim 10, whereinthe formulation comprises a composition (X) comprising the at least onecopolymer (A), and the at least one organic solvent (B), wherein theconcentration of the copolymer (A) is 5 to 25% by weight with respect tothe sum of all components of the composition (X).
 12. The methodaccording to claim 10, wherein the formulation used additionallycomprises at least one wax dispersant.
 13. The method according to claim12, wherein the wax dispersant is at least one selected from the groupconsisting of alkylphenols, alkylphenol-formaldehyde resins, anddodecylbenzenesulfonic acid.
 14. The method according to claim 11,wherein the organic solvent (B) comprises a hydrocarbon or a hydrocarbonmixture.
 15. The method according to claim 11, wherein the solvent (B)comprises saturated aliphatic hydrocarbons having a flashpoint≥60° C.16. The method according to claim 11, wherein the concentration of thecopolymer (A) is 10 to 20% by weight.
 17. The method according to claim10, wherein the amount of copolymer (A) added is 50 to 3000 ppm of thecopolymer (A) based on the crude oil.
 18. The method according to claim10, wherein the formulation is injected into a crude oil pipeline. 19.The method according to claim 10, wherein the formulation is injectedinto a production well.
 20. A method comprising adding a rheologymodifier comprising at least one formulation comprising a copolymer (A)and an inorganic solvent to crude oil; wherein the copolymer (A)comprises (M1) 83.5 mol % to 96.5 mol % of ethylene, (M2) 3 mol % to11.5 mol % of at least one vinyl ester of the formula H₂C═CH—O—(O)C—R¹(I) where R¹ is H or a C₁- to C₄ alkyl moiety, and (M3) 0.5 mol % to 5mol % of a (meth)acrylate of the formula H₂C═C(R²)—COOR³ wherein R² is Hor methyl, and R³ is selected from the group consisting of R^(3a):branched alkyl moieties having 4 to 18 carbon atoms, R^(3b): cyclicalkyl moieties having 5 to 12 carbon atoms, and R^(3c): aryl moietieshaving 6 to 12 carbon atoms which are optionally alkyl substituted , andwherein the copolymer (A) has a weight average molecular weight M_(w) of35,000 g/mol to 150,000 g/mol.
 21. The method according to claim 20,wherein the formulation comprises a composition (X) comprising the atleast one copolymer (A), and the at least one organic solvent (B),wherein the concentration of the copolymer (A) is 5 to 25% by weightwith respect to the sum of all components of the composition (X).